You're on a network with only HTTP/HTTPS access to the internet... you've got OpenVPN setup to tunnel all your traffic out via HTTPS.... but you still want to access the local LAN?

All the OpenVPN client is doing is changing the routing table on the OS (netstat -nr / route print) you'll see that the route to the OpenVPN server is in there and the default gateway is the OpenVPN tunnel interface, to connect to the local LAN simply add a route via the "local gatway", i.e. the same gateway used to get to the vpn server.